The overall objective of this proposal research is to study nuclear function and the regulation of gene activities in P. aurelia and is directed toward the use of Paramecium as a model system in the study of cellular aging and differentiation. Like most cells which undergo senescence, paramecia exhibit increased generation times as fission age increases, diminished ability to repair and replicate DNA, and accumulation of aging pigments. These biological and biochemical alterations could be primary events in the development of senescence or could reflect other more direct consequences of cell aging. Using Paramecium as a model system presents an opportunity to relate changes which occur with aging to specific functions as well as to the complete organism. Paramecia offer the particular advantage of having a life span potential of about 300 fissions and rejuvenation of aging cell lines can be readily accomplished by allowing autogamy to take place. A proposed target for the aging process is the protein synthetic machinery of the cell. While this process is complex and one of many stages could misfunction in the aged cell, we have chosen to focus on the RNA components with an emphasis on mRNA. Our approach will be to: 1) determine the molecular weight species of proteins and classes of mRNA synthesized in vivo; 2) study the translation properties of ioslated mRNA in an in vitro system and compare with that found in vivo. This will include studying poly A(plus) and poly A(minus) containing messages as well as the effect of tRNA and ribosomes in a heterologous system; and 3) investigate in vivo expression of specific surface antigen proteins by micro-injection of isolated mRNA. These studies will be done as a function of growth state as well as cell age and may yield important information concerning the general basis for the expression of mRNA in both unicellular and multicellular eukaryotic organisms.